1. Field of the Invention
The present invention relates to the atomization of a liquid, and more particularly, to an inhaler device with a removable dosating unit for delivering precise amounts of medicament to an ultrasonic atomizer device for atomizing the medicament for inhalation by a patient.
2. Description of the Prior Art
Liquid atomizers are well known and come in several types, including aerosol, manual and ultrasonic. For example, there are aerosol atomizers for various applications, such as dispensing cosmetic and hygienic products (hair spray, deodorant, etc.) and cleaning solutions (disinfectants, air fresheners, etc.). Aerosol atomizers can also be used for dispensing medicaments although they have significant drawbacks when used for that purpose. For one thing, they dispense medicaments at a high velocity, which can adversely affect a patient's ability to coordinate dispensing and inhaling the medicament. Moreover, medicament atomized and dispensed by aerosol is usually very cold and can irritate the patient's throat, and the aerosol propellant may have adverse affects on the patient as well as on the environment.
Manual atomizers are also available. In this type of device, the medicament is dispensed by a manual force provided by the patient to atomize the medicament. The most significant advantage of such atomizers is their simplicity, which makes them capable of being made small enough to be carried by patients and thus be readily available for use at any time.
However, difficulties with purely manual atomizers include non-uniformity of dosage from one patient to another (since different people will inevitably use different amounts of force to operate the device and because such devices sometimes deliver different dosages from one use to another), difficulty in coordinating the required manual actuation and inhalation of the expelled medicament (a problem particularly with very young and very old or infirm patients) and inability to protect the medicament from contamination.
Ultrasonic atomizers include one type using a piezoelectric element to atomize a liquid medicament deposited thereon by manually moving a piston within a cylinder containing the medicament to be atomized. The piston forces the liquid from an outlet in the cylinder, which deposits it onto the piezoelectric atomizer, which in turn is activated as part of the manual medicament-dispensing operation.
Examples of this type of ultrasonic atomizer (using a manually dispensed medicament) are shown in U.S. Pat. No. 4,294,407, U.S. Pat. No. 4,877,989 and U.S. Pat. No. 5,134,993. Although such atomizers are better in some respects than their purely manual counterparts, they do not completely solve the problem of providing a uniform dosage under all conditions and for all patients, and they are limited in the amount of medicament that can be atomized because of power considerations relating to the piezoelectric ultrasonic atomizer.
An ultrasonic atomizer is also proposed in European Patent Application EP 0 689 879 A1.
Another type of ultrasonic atomizer includes a pump to deliver liquid from a reservoir to a piezoelectric vibrator. Examples of this type of device are shown in British Patents No. 1,434,746 and No. 2,099,710 and European Patent Application EP 0 569 611 A1. These devices are capable of better uniformity in the amount of liquid atomized at each actuation, but they still have significant drawbacks as portable medication-delivery systems. For example, the atomizers shown in British Patents No. 1,434,746 and No. 2,099,710 clearly would be difficult to miniaturize sufficiently to make them small enough to carry in a patient's pocket or purse for convenient or, in the case of an asthma sufferer, emergency use. Further, the technique in British Patent No. 2,099,710 for dispensing the liquid to be atomized, by crumpling the liquid container, does not allow sufficient dosage precision because of the unpredictability of exactly how the container will deform.
On the other hand, the atomizer of EP 0 569 611 A1 is specifically designed to be a fully-portable, hand-held atomizer for medicament fluids such as bronchospasmolytic agents used to treat asthma. And while it is a significant advance over previously known devices, it, too, has proven unsuitable for various reasons.
A principal problem is the peristaltic tube pump disclosed in EP 0 569 611 A1 as the mechanism for delivering the medicament liquid to the piezoelectric atomizer. Although it is more precise than prior delivery systems, it still is subject to large variations in the amount of liquid it delivers. This is the result of several factors. One such factor is that any bubbles which form in the tube can significantly affect dosage amounts because those amounts are so small. Second, manufacturing tolerances in the tube diameter can also significantly affect dosage amounts for the same reason. EP 0 569 611 A1 also discloses a spring-valve system for pressurizing the liquid storage container and metering fluid therefrom, instead of the tube pump, but that still does not provide the precision dosing required in many applications, such as in a medical device, and is unduly complicated.
The device in EP 0 569 611 A1 has other drawbacks as well. The dosating system, containing the pump (or the spring-valve system) and medicament reservoir, is fairly large, and when attached to the device forms a significant part of its outside envelope. As such, it is prone to becoming detached when the unit is carried in a pocket or purse. In addition, the dosating system is difficult to seal in a manner that maintains suitable microbiological conditions over long periods. Finally, any medicament remaining after actuation at the end of the tube delivering it to the piezoelectric element will be exposed to the atmosphere until the next actuation, and thus be prone to contamination. Because that potentially contaminated medicament is then atomized and inhaled by the patient in the next actuation, it is necessary to address that issue from the standpoint of patient safety.
In addition, all types of prior ultrasonic atomizers suffer from the problem of being unable efficiently and effectively to atomize sufficient amounts of medication. For example, a piezoelectric element of a certain size can only atomize a given amount of liquid on its surface. If that is a smaller amount than the dosage amount for a particular medicament, then the atomizer will be inherently incapable of performing its intended function as an inhalable-medication delivery system. Making the piezoelectric element larger is a potential solution, but the amount of power required to operate a piezoelectric element at a given frequency increases exponentially as the size of the element increases. Accordingly, the size of the piezoelectric element is perforce limited because the atomizer, to be practicable, must be capable of a significant number of operations using batteries small enough to fit into a pocket-size device.